Edexcel A-Level Biology: Cells, Viruses and Reproduction
6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
A liver cell is highly active: it synthesises and secretes large amounts of protein (such as plasma proteins) and carries out many energy-demanding reactions.
Describe and explain how the structure of the following organelles enables a liver cell to synthesise and secrete proteins and to meet its high energy demand: the nucleus, the rough endoplasmic reticulum, the Golgi apparatus and mitochondria.
(6 marks)
A student used a transmission electron micrograph to compare the size of a mitochondrion with that of a ribosome. They measured the length of each structure on the printed image and recorded the magnification stated in the figure caption.
| Structure | Length on image / mm | Magnification of image |
|---|---|---|
| Mitochondrion | 30 | ×15000 |
| Ribosome | 5 | ×250000 |
The equation linking magnification, image size and actual size is:
magnification=actual sizeimage size
(a) Calculate the actual length of the mitochondrion. Give your answer in micrometres (μm) and show your working. (3 marks)
(b) The student concluded: 'The ribosome looks smaller than the mitochondrion on the image, so the ribosome must be the smaller structure.' Using a calculation of the actual length of the ribosome, explain whether the student's conclusion is correct. (3 marks)
A student investigated osmosis using cylinders cut from a potato. Five cylinders of equal initial mass were each left for 30 minutes in a sucrose solution of a different concentration, then reweighed. The results are shown below.
| Sucrose concentration / mol dm⁻³ | Initial mass / g | Final mass / g |
|---|---|---|
| 0.0 | 5.00 | 5.40 |
| 0.2 | 5.00 | 5.15 |
| 0.4 | 5.00 | 5.00 |
| 0.6 | 5.00 | 4.70 |
| 0.8 | 5.00 | 4.45 |
(a) Calculate the percentage change in mass of the cylinder placed in the 0.8 mol dm⁻³ solution. Show your working. (2 marks)
(b) Identify the sucrose concentration at which the solution was isotonic with the potato tissue, and explain how the data support your answer. (3 marks)
Cells lining the kidney tubule reabsorb glucose from the tubule fluid back into the blood, even when the glucose concentration inside the cell is already higher than in the tubule fluid.
A researcher treated samples of these cells in three ways and measured the rate of glucose reabsorption:
- Treatment 1: a chemical that stops mitochondria producing ATP was added → reabsorption almost stopped.
- Treatment 2: the number of carrier proteins in the cell-surface membrane was experimentally increased → reabsorption rose sharply.
- Treatment 3: the temperature was raised from 20 °C to 40 °C → reabsorption increased, then fell as the temperature rose further.
Suggest and explain what these three results reveal about the mechanism by which glucose is reabsorbed by these cells. (5 marks)
A species of lizard can reproduce in two ways. In some populations, females reproduce asexually: unfertilised eggs are produced by mitosis and develop into offspring. In other populations, the lizards reproduce sexually, with eggs and sperm formed by meiosis and combined at fertilisation.
A disease caused by a new parasite spreads through the region.
Explain why the sexually reproducing populations are likely to be more able to survive the new parasite than the asexually reproducing populations. (4 marks)
Viruses, such as the human immunodeficiency virus (HIV), are described as acellular and are not classed as either prokaryotic or eukaryotic cells.
Describe three structural features that are present in all viruses. (3 marks)